Fermi-surface and charge-spin excitations in strongly correlated electron systems

T. McMullen

Several experimental techniques, such as photoemission, Compton scattering, and positron annihilation, use the excitation or destruction of an electron to measure the momentum distribution of the electrons. The structure in these momentum distributions that results from the Fermi surface of a Fermi liquid is well known, but structure can also arise from the electron correlations in a strongly correlated system. The momentum distribution of a highly correlated two-dimensional electron system in which the spin and charge degrees of freedom are decoupled is examined using, as a model system, a noninteracting spinon-holon description of the excitations of the two-dimensional Hubbard model.

A. P. Protogenov

Sadamichi Maekawa, Takami Tohyama, Seiji Yunoki

Alan H. Luther

Electronic states near a square Fermi surface are mapped onto quantum chains. Using boson-fermion duality on the chains, the bosonic part of the interaction is isolated and diagonalized. These interactions destroy Fermi-liquid behavior. Nonboson interactions are also generated by this mapping, and give rise to an alternate perturbation theory about the boson problem. A case with strong repulsions between parallel faces is studied and solved. This solution discards irrelevant operators in a new interaction Hamiltonian. There is spin-charge separation and the square Fermi surface remains square under doping. At half-filling, there is a charge gap and insulating behavior together with gapless spin excitations. This mapping appears to be a general tool for understanding the properties of interacting electrons on a square Fermi surface.

Pavel V. Shevchenko

K. P. Jain, D. K. Ray

An approximate expression has been derived for the wave number and frequency-dependent spin susceptibility \ensuremath{\chi}(q,\ensuremath{\omega}) for a system of strongly interacting electrons when the charge and spin degrees of freedom can be separated. This expression has contributions from particle-hole excitations across the pseudo-Fermi surface of the quantum spin fluids as well as from pair excitations.